The invention relates to a hand-held power tool, specifically an impact drill or hammer, particularly with an electric drive motor for the rotatory drive via a transmission, of a rotating sleeve impinging upon a tool holder in which a tool can be guided, and by means of which electric motor an impacting mechanism can also be driven. The impacting mechanism has an axially oscillating drive piston, an impactor actuated by the drive piston through an air cushion, the impactor imparting its impact energy to the tool, and also a translation drive acting on the drive piston. The translation drive has, on its part, a drive member which preferably can be driven in a rotary motion and is provided with a guide curve and at least one actuator which follows the guide curve and which will effect an axial displacement of the drive piston.
Such a hand-held power tool is known from DE Letter of Disclosure No. 244 9191. Therein, the drive motor, through a motor pinion engaging a gear, drives a swash plate being a component of an impacting mechanism, located, rigidly mounted, on an intermediate shaft, the latter on its part bearing a further gear engaging a gear provided on the rotary sleeve. The rotary sleeve in turn is also provided with gearing which engages the gearing at the offset of the tool holder thus effecting its rotatory drive. Thus, four gears are required at the side of the transmission, and furthermore two additional gears at the rotary sleeve and the offset subordinated to it. This plurality of gears is expensive, requires very much space within the machine, and will thus cause it to become costly overall, relatively large as well as heavy and, therefore, unwieldy. As for the transmission, it is a further disadvantage that the expenditure for bearings for all transmission components described, is considerable, and this also exerts a disadvantageous effect upon price, dimensions, and weight, of the machine.
The translation drive with its impacting mechanism also has numerous disadvantages. The transmitting member is represented by the swash plate which has a circular groove as its guide curve, running crosswise, but at an incline, to the drive axis of the swash plate. Located within this circular groove and rotatory relative to the swash plate is a ring as an actuator, having a projecting actuator pin acting upon a piston pin of the drive piston. The drive piston is non-rotatory. This construction of an impacting mechanism with translation drive is very expensive and will lead to relatively high manufacturing cost. Furthermore, it will require considerable space within the machine. It has an additional disadvantage that the force effecting the axially oscillating motion of the drive piston acts eccentrically onto the drive piston, thus subjecting the longitudinal guide to additional stress and additional wear.
One rotation of the swash plate as drive member will effect one axial blow upon the tool. For the attainment of a high number of blows, the swash plate must be driven at a relatively high speed. Since, on the other hand, the swash plate is subjected to stresses caused by strong forces, it must be so designed that it can sufficiently withstand such stresses also over a longer period. This will result in a solid and heaavy construction of the swash plate with the actuator guided on it. Thus, a relatively large rotating mass will result in this zone. In other respects, this construction is expensive and will also bring about a high weight of the machine.